Product Feature: Bioclimatic Air Systems manufactures air purification units. Their web site is www.bioclimatic.com
By utilizing Bioclimatic's air purification technology and ASHRAE Standard 62 Indoor Air Quality Procedure, the outside air may be reduced to a minimum of 5 CFM per person in most applications, provided building pressurization is still achieved. The reduction in outside air reduces the refrigeration load and heating load on the building. The equipment costs associated with the reduction in the cooling and heating loads offsets the price of the Bioclimatic equipment and offers the owner capital cost savings in most applications. In addition to the first cost savings, lower operating costs and improved IAQ will be achieved. Variable Volume DX Systems: One of the disadvantages of DX packaged or split systems has been control of the coil temperature. The compressors cycling on/off so you get an average coil temp in DX packaged or split system, where in a chill-water system you can modulate the control valve at the air-handler to get a consistent coil temperature. I offer a variable flow DX system that takes advantage of technology that is being used here in N.Al on several jobs that uses a digital scroll compressor to vary the refrigerant flow to the coil keeping it at a consistent temperature. Why is this valuable? With variable refrigerant flow you can adjust for any differences in inlet to outlet coil temperatures, eliminates HGBP, and if the system was oversized, no problem! The cost you ask? On a recently selected 25-ton MAU/RTU unit it was only a 5% increase over a unit without a digital scroll compressor! The cost saving in energy alone will be a quick payback, but the real cost saving is the ability to combine your MAU and RTU into one unit! Designing Outside Air Units: Some considerations when designing outside air units:
Two main consideration in sizing a unit: What is the OA cfm needed & what is the unit discharge dewpoint desired?
OA Design Rule-O-Thumbs: 200cfm/ton
Relative humidity is relative! You can raise or lower the RH% by increasing or decreasing the room temperature but the moisture in the air stays the same. Ex: 86F & 50%rh has the same amount of moisture in the air as 65F & 100%rh. Design around how much moisture is allowed in the air or a dewpoint temp! Do not design around relative humidity! Is the unit going to provide neutral air or condition air to the space? (state which type of system is desired in specs) Neutral Air = Take OA and treat it to a set temp & humidity (ex: 72F @ 55%rh), supply sensors at discharge of unit. - PRO: consistent control/comfort, no sweating in space/duct work. CON: 2 independent systems, OA treatment & Zone comfort Condition air to zone = Take OA and meet setpoints in zone, supply sensors in the zone - PRO: 1 system. CON: unit has to treat OA from 100F to 20F at different humilities, and provide a consistent space temp & humidity. Look at several different OA conditions other than design: Ex: 95/75, 83/77.5, 65/65 (at this temp the suction temps tend to go below limits and the unit will either cycle on/off therefore ensure you have hot-gas bypass), 20/15.
Calculating Sensible and Latent Heat: We begin a four part series involving calculating sensible and latent heat from persons, electric equipment, machines, lights, evaporation from water surfaces, polluting fluids and miscellaneous loads The indoor climate is influenced by sensible and latent heat from persons, lights, machines and electrical equipment and industrial processes pollution and gases from persons, building materials, inventory and industrial processes The most important sources may be summarized as:
- Sensible and latent heat from persons
- Sensible heat from lights
- Sensible heat from electric equipment
- Sensible heat from machines
- Latent heat from evaporation from water surfaces
- Evaporation from polluting fluids
- Miscellaneous loads Sensible and latent heat from persons: Sensible heat from persons are transferred through conduction, convection and radiation. Latent heat from persons are transferred through water vapor. The sensible heat influence on the air temperature and latent heat influence the moisture content of air.
The heat transferred from persons depends on their activity, clothing, air temperature and the number of persons in the building. Sensible heat from machines:
When machines runs heat can be transferred to the room from the motor and/or the machine.
If the motor is in the room and the machine is outside the heat transferred can be calculated as
Hm = Pm / hm - Pm
Where:
Hm = heat transferred from the machine to the room (W)
Pm = electrical motor power consumption (W)
hm = motor efficiency
If the motor is belt driven and the motor and belt is in the room and the machine is outside the heat transferred can be calculated as Hm = Pm / hm - Pm hb
Where:
hb = belt efficiency
If the motor and the machine is in the room the heat transferred can be calculated as
Hm = Pm / hm
In this situation the total power is transferred as heat to the room.
Note! If the machine is a pump or a fan, most of the power is transferred as energy to the medium and may be transported out of the room. If the motor is outside and the machine is in the room the heat transferred can be calculated as
Hm = Pm
If the motor is belt driven and the motor and belt is outside and the machine is in the room the heat transferred can be calculated as Hm = Pm hb
When Do I Need Lightning Protection For My Controls System? It's a good question to ask before selling or starting up a new control system. This is rarely given much attention by owners, engineers, or sales people. Be aware in certain types of installations, if lightning protection devices are not used, even an indirect lightning strike can cause substantial and costly damage to your controls system installation.
If the control system is contained within a single building that has proper electrical grounding, you will rarely encounter a problem with lightning as most nearby lighting strikes will be dissipated through the building grounding system and direct lightning strikes to most buildings are extremely rare. Building protection from direct lightning strikes requires a sophisticated lightning protection system engineered and installed by lightning protection consultants. Generally the expense for this type of lightning protection limits its use to very tall buildings or buildings in areas where direct lightning strikes are a known problem. So when is it critical to use lightning protection?
Anytime you have a multi-building installation and the communication cable enters or exits a building, lightning protection is absolutely required! Cabling exposure, either above or underground, acts like an antenna picking up induced voltage/current surges from localized lightning strikes from up to several miles away. When you have multiple buildings with communication cabling between them, these voltage surges will damage your controls system if it is not adequately protected with RS-485 data line lightning surge protectors properly installed in the communications line. For these multi-building types of installations, a surge protector must be installed just before the communication cable exits one building and again when it enters the next building. Please be aware that all surge protection is not created equal! Some cheaper RS-485 surge protectors do no more than filter noise on the loop without providing any real protection from transient spikes. It is important that the surge protector be connected to a quality building "ground". If there is no ground connection, the spike has no place to go. It will then follow the path of least resistance which is usually your equipment. The surge protector also needs the ability to "self restore" after a spike so you don't have to replace the surge protector every time a spike occurs. It is important to understand that no surge protector can provide a 100% guarantee that your equipment will never be damaged. But with multi-building installations without one you are guaranteed to have problems. Damage caused by voltage/current surges are not covered under most product warranties.
Useful Formulas: Total Heat (BTU/hr) = 4.5 x cfm x ∆h (std. air) Sensible Heat (BTU/hr) = 1.1 x cfm x ∆t Latent Heat (BTU/hr) = 0.69 x cfm x ∆gr. (std. air) Total Heat (BTU/hr) = 500 x gpm x ∆t (water) BTU/hr = 3.413 x watts = HP x 2546 = Kg Cal x 3.97 TONS = 24 x gpm x ∆t (water) GPM cooler = (24 x TONS) / ∆t (water) Fluid Mixture Tm = (Xt1 + Yt2) / X + Y (this works for air or water) Lb. = 453.6 grams = 7000 grains psi = ft. water/2.31 = in. hg/2.03 = in. water/27.7 = 0.145 x kPa Ton = 12,000 BTU/hr = 0.2843 x KW HP (air) = cfm x ∆p (in.H2O)/6350 x Eff. HP (water) = gpm x ∆p (ft.)/3960 x Eff. Gal. = FT3/7.48 = 3.785 Liters = 8.33 lb. (water) = 231 in. 3 gpm= 15.85xL/S cfm = 2.119 x L/S Liter = 3.785 x gal = 0.946 x quart = 28.32 x ft3 Therm = 100,000 BTU = MJ/105.5 Watt/sq. ft. = 0.0926 x W/M2 yd. = 1.094 x M ft. = 3.281 x M ft2 = 10.76 x M2 ft3 = 35.31 x M3 ft/min = 196.9 x M/S PPM (by mass) = mg/kg
NOTE: Liter/sec is the proper SI term for liquid flow. M3/sec is the proper SI term for airflow. Due to the awkward nature of using M3/S at low air flow rates (lots of decimal points), L/S is commonly used to express air flow for HVAC applications.
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